The present invention relates to the application of coating or sizing material to fibers. The sizing material is usually of the type applied to fibers that are to be used as a reinforcement. The apparatus of this invention applies the sizing to glass filaments at forming.
The technology which has been developed for the production of glass fibers, presently makes possible the production of fibers having a diameter of from approximately 0.0001 inch to approximately 0.0004 inch, at a rate of from approximately 4,000 feet per minute to approximately 15,000 feet per minute. Glass fibers are produced from small streams of molten glass which exude through tiny orifices located in what is called a forming position. The tiny steams of molten glass which issue from the bushing are attenuated by pulling the fibers until the diameters given above result, and during which time the streams cool and rigidify into what are called filaments. These filaments are then coated with a protective film for the purpose of preventing glass to glass abrasion, and following which they are brought together to form a strand. This strand is coiled upon a tube to form a package. During formation of the package, the strand is traversed back and forth across the tube by a device which is called a traverse, and which is located between the point where the coating materials are applied, and the rotating tube on which the package is made. The tube is rotated by what is called a collet, and the pulling action supplied by the collet attenuates the molten streams of glass, pulls the filaments past the coating applicator, and through the traverse, and coils the strand onto the package. The winder is usually located approximately 10 feet from the bushing, so that the entire forming operation is carried out in a fraction of a second.
The problem of abrasion of glass upon glass is a serious one and has generally been a controlling factor in the rate at which this technology has developed. The seriousness of this problem has caused the wide spread theory that glass on glass abrasion can only be prevented by a solid film of material between the filaments to at all times assure physical separation of the filaments. The coating on the filaments is usually as a liquid during the filament forming operation.
Roll type applicators have been used frequently in the past to coat filaments to protect them from glass upon glass abrasion. The applicator has a rotating roll that is patially submerged in coating material that is held in a container positioned below the roll. As the roll rotates it keeps picking up a fresh supply of coating liquid from the container. This liquid is carried on the roll until it is removed by filaments that pass across the roll. As the filaments remove the liquid they become coated with the liquid. This is a continuous process that does a good job of coating the filaments.
When filaments that are formed at high speeds are being coated the relationship between the liquid container and the applicator roll must be carefully controlled. This is because a great deal of air may be carried along with the filaments and this air can find its way into the liquid container. The air can cause turbulence in the liquid and can even blow the liquid out of the container. This of course greatly disrupts the coating operation and can waste a great deal of coating liquid.
To control the air problem it has been customary to design the applicator so that there is a very small space between the roll and the liquid container, on the filament coating side of the applicator. The small space allows the applicator to rotate but helps to keep air from entering into the liquid container.
The problem with this solution to the air problem is that the filaments usually wear grooves in the applicator roll. When this happens the roll must be removed and machined until it is smooth again so that it will properly coat the filaments. However, the machining removes material from the roll and the roll cannot be machined too many times before it becomes considerably smaller than its original dimension. As the roll gets smaller from machining the space between the roll and the liquid container gets larger. After the roll has been machined a few times the space becomes so large that it no longer will help to prevent the air carried with the filaments from entering into the liquid container. When this happens the old stationary roll must be removed and replaced with a new roll. The old roll is no longer suitable for use even though there is a lot of useable material left on the roll.
This type of applicator is expensive to operate because it requires the rolls to be replaced so frequently and such a small portion of the roll is used. This type of applicator also has no provision for using different size applicator rolls in the coating process.